AAV On Sink /Wet Vent for Toilet? With Diagram

Wow, been a while since I've been on this awesome forum. Decided to add a small bar sink in a "butler's pantry" we're working on, stealing the cold water from a powder room toilet that is just on the other side of the wall where we're planning to put the sink.

But in the process, discovered the toilet does not have a vent as I understand it. (Toilet works fine, BTW).

So am thinking of adding an Air Admittance Valve on the bar sink, that would act as a wet vent for the toilet. Could actually also go up with a roof vent, but would have to tear out a bunch of sheetrock, make a bend and go thru a double roof....

So here is the general idea of what I think would solve the problem - NEW PROPOSED CONNECTION IN GREY: - Will this work to vent both toilet and sink?
(I took the liberty of modifying someone else's diagram I found on the forum I hope that's OK!)

A toilet will work just fine without a vent...and, in your situation, it wouldn't affect any of the pre-existing devices, because they all have vents. Most inspectors won't approve an AAV unless it is the best solution of a bad situation. If possible, you might attach the new sink's vent to one of the others to the right in your diagram. It would need to be made at 42" or higher above the floor and there are limits on how many turns it can take plus, it must still be sloped back to the drain.

An AAV only lets air in. With it in that location, when you flushed the toilet, there's a pressure wave in front of the wave as the stuff flows down the pipe. That would want to push stuff to the point of least resistance. It probably wouldn't spit out the new sink, but since the AAV can't let that pressure wave out, it likely would rock the water in the trap.

Thanks for replies. I should have mentioned I'm in WA State, I read some King County code that said an AAV is OK.

So Terry, I believe you are saying the new grey connection with AAV is OK as drawn - that's great!

And the part on the right is weird in part because that section of the house was built in 1965 with a sort of strange beam construction and there have been about 2 remodels since then, the nearer 2" roof vent is no longer in use, the crawl space is just about big enough for a kid so clearance is an issue... Plus my drawing skills kind of gave out on that side But the connections are as documented.

I could also continue the new sink drain straight up thru the roof at that point to vent, or make a right bend at 42" go up to attic right bend again and attach to the abandoned vent before it exits the final roof. But that's a lot more construction work for an 8" bar sink...

This house is on an old septic system too, Oatey's warning is "The use of an AAV with septic systems requires no special considerations other then that the “primary vent” to open air MUST be located at the point of heaviest drainage loading or taken off from the lowest building drain elevation (downstream from all other drainage)."

If we do a roof vent, I realized going straight up is probably not an option after all, too close to roof eave so have to make a bend. And the abandoned vent is 14 feet away so I don't think we can tie into that, still have to go out the roof after making a bend.